A Greek black metal band. Does it honsetly matter whether they are "true" or not? It's a band making its own music, that's it. The same goes for everything else extreme closed-minded philistines don't like purely based on popularity reasons instead of the music itself.
Yes, Norway probably did invent the genre, but in the same way that the UK invented the telephone, it can be made in other countries just as well, sometimes better. My phone's Japanese, for example, although Alex Bell invented the first one.
Rotting Christ is a rather good Greek black metal band.